This invention relates to a fluid displacement apparatus, and more particularly, to an axial sealing mechanism for a scroll type fluid displacement apparatus.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 issued to Creux discloses apparatus including two scroll members each having a circular end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the line contacts long the spiral curved surfaces and, therefore, the fluid pockets change in volume. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbiting motion, this scroll type fluid displacement apparatus is applicable to compress, expand or pump fluids.
In comparison with conventional compressors of the piston type, a scroll type compressor has certain advantages, such as fewer parts and continuous compression of fluid. However, one of the problems encountered in prior art scroll type compressors has been ineffective sealing of the fluid pockets. Axial and radial sealing of the fluid pockets must be maintained in a scroll type compressor in order to achieve efficient operation. The fluid pockets in a scroll type compressor are defined by line contacts between the interfitting spiral elements and axial contacts between the axial end surfaces of the spiral elements and the inner surface of the end plates.
One solution to the axial sealing problem is described in copending application Ser. No. 588,563, filed on Mar. 12, 1984. In the scroll type apparatus of this prior application, as shown in FIGS. 1 and 2, the end surface of each spiral element 1 which faces end plate 2 of the other scroll member is provided with groove 3 formed along the spiral. Seal element 4 is closely fitted within groove 3. Seal element 4 has an axial dimension greater than the depth of groove 3 so that, before spiral element 1 is placed in an interfitting position with another spiral element, seal element 4 projects from spiral element 1 by predetermined amount "y". Since predetermined amount "y" is greater than axial gap "t" between the axial end surface of spiral element 1 and end plate 2' of the other scroll member, when both spiral elements 1 are placed in their interfitting positions as shown in partial cross-section in FIG. 2, seal element 4 maintains contact with the facing end plate 2' of the opposing scroll member without the use of any axial force urging device.
A disadvantage of the above construction is that seal element 4 should be urged toward the facing scroll member by a greater force to accomplish effective sealing. In the above construction of the axial sealing mechanism, the seal element should be deformed by compression of the facing end plate to absorb the cumulative error of assembly of the scroll members and to accomplish effective axial sealing along the length of the seal element. As a result, the seal element in this prior construction must be formed of very soft material to enable the deformation of the seal element in accordance with the change of axial gap "t" between the spiral element and the facing end plate.